The isolation of hepatitis B surface antigen from plasma and its purification and use in a vaccine to immunize against hepatitis B is known and is described, for example, in U.S. Pat. Nos. 3,636,191 and 4,017,360. Current vaccines isolated from plasma, however, do not contain the preS2 component of the hepatitis B surface antigen. An antigen containing the pre-S region would have enhanced immunogenicity relative to antigens produced by current techniques which lack this region of HBsAg.